1. Field of the Invention
This invention generally relates to microwave power sensors and, in particular, to such sensors which are constructed integrally with a monolithic circuit substrate.
2. Statement of the Prior Art
Various devices have been used for sensing microwave power. Such devices typically use one of a variety of sensors for converting microwave energy into heat and measuring the resulting temperature. Known devices include Wallaston wires, thermistors and thermocouples mounted in waveguides and coaxial transmission lines. Typically the sensing element is used as a microwave termination requiring that the microwave characteristics of the sensing element be matched to the circuitry or vice versa. For this reason, the sensing elements must be designed to have a low VSWR within the waveguide or coaxial mounting and must also have a temperature dependent electrical characteristic. Because of these requirements, power sensors which are operable over very broad frequency bands have not previously been developed.
Further, the minimum size of such sensors is often limited by the need to obtain sufficient temperature sensitivity. The various sensors have a measurable electrical sensitivity to temperature changes. Wires and thermistors vary in conductivity and thermocouples vary in output voltage. If the length of a wire or thermistor is small or the area of dissimilar metal junction of a thermocouple is small, the amount of change in the respective measurable electrical characteristic will also be small. This results in less sensitivity for determining temperature as the size of the sensing element is reduced, and an inherent limitation on the minimum size of such sensors.
Also, as the use of microwaves in communications and surveillance increases, so does the demand for performance at higher and higher microwave frequencies. This performance is inhibited in traditional circuit components by increases in their reactive impedances attributable to the higher operating frequencies. As reactive impedance is proportional to component size, there is a constant need for research and development of smaller circuitry, components, and devices to enable higher frequency performance.